The present invention relates to a rotation angle detecting device for detecting the angle of rotation of a rotary member such as a vehicular steering shaft, and to a torque detecting device for detecting a torque to be applied to the rotary member, and a method of manufacturing the rotation angle detecting device.
As an auxiliary steering device mounted on a vehicle such as an automobile for assisting the steering operation of a driver, there is an electric power steering device for applying the turning force of an electric motor, for example, as steering assisting force. This electric power steering device is provided with an input shaft and an output shaft, which are so connected to a steering member and steering wheels side, respectively, as to rotate according to the steering operation of the driver. Into this steering device, moreover, there are incorporated a rotation angle detecting device including sensor units for detecting the respective rotation angles of the input and output shafts, and a torque detecting device for detecting the steering torque to be applied to the steering member by using the detection results of the detecting device. The steering device assists the steering operation by deciding an instruction value to the electric motor on the basis of the detected steering torque and by transmitting the motor turning force to a steering system through a reduction mechanism thereby apply the steering assisting force to the steering system.
Moreover, the sensor unit of the rotation angle detecting device is provided with targets made of magnetic members and mounted integrally rotatably on the respective input and output shafts, and magnetic sensors including magnetoresistive effect (MR) elements arranged to confront at a predetermined gap on the outer circumferences of the targets, for outputting output signals varying periodically according to the rotations of the corresponding input and output shafts. In this sensor unit, two regions of a linear region in which the outputs of the sensors linearly change and a nonlinear region in which the outputs nonlinearly change appear according to the circumferential shape of the targets. Therefore, the sensor unit is constructed to obtain a common output waveform for two channels different each other only in phase by providing two magnetic sensors for both the input and output shafts and by arranging those sensors with a shift in the circumferential direction of the corresponding target. In this detecting device of the related art, the detecting precisions of the respective rotation angles of the input/output shafts are prevented from degrading (as referred to Patent Publication 1, for example) by using the respective outputs of the two channels so that the outputs are supplemented each other so as to detect the rotation angle at all times by using the sensor outputs in the linear regions (See, for example, JP-A-2002-82002).
However, in case the rotation angle detecting device of the related art uses the semiconductor MR elements as the aforementioned MR elements, the outputs of two channels of the two semiconductor MR elements may fail to have the aforementioned identical waveforms different each other only in phase due to the material difference of the semiconductor MR elements. More specifically, in this detecting device of the related art, a one-chip sensor having the MR elements formed in one cell of the semiconductor wafer is used as the MR element for each channel, and either two sensor chips of different rod numbers of the semiconductor wafer or two sensor chips formed in cells at mutually spaced positions over a common wafer may be combined and used as the MR element of two channels. Therefore, these MR elements of two channels may not have identical electric characteristics such as temperature characteristics due to the material difference of the MR elements. In case the MR elements are arranged at positions shifted in the circumferential direction of the targets, therefore, the waveforms of the outputs of the two channels may be different not only in the phase but also in the amplitude or the like.